#2324939 Theme initialization was moved into its own service

from:
  fqn: 'fn:drupal_theme_initialize'
to:
  fqn: '\Drupal\Core\Theme\ThemeManager::getActiveTheme'
to:
  fqn: '\Drupal\Core\Theme\ThemeManager::setActiveTheme'
to:
  fqn: '\Drupal\Core\Theme\ThemeInitialization::initTheme'
to:
  arg: 0
  fqn: '\Drupal::service'
  string_in:
    - theme.manager
    - theme.initialization